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Human immunodeficiency virus (HIV) vaccines have not been successful in clinical trials. Dimeric IgA (dIgA) in the form of secretory IgA is the most abundant antibody class in mucosal tissues, making dIgA a prime candidate for potential HIV vaccines. We coupled Positron Emission Tomography (PET) imaging and fluorescent microscopy of 64Cu-labeled, photoactivatable-GFP HIV (PA-GFP-BaL) and fluorescently labeled dIgA to determine how dIgA antibodies influence virus interaction with mucosal barriers and viral penetration in colorectal tissue. Our results show that HIV virions rapidly disseminate throughout the colon two hours after exposure. The presence of dIgA resulted in an increase in virions and penetration depth in the transverse colon. Moreover, virions were found in the mesenteric lymph nodes two hours after viral exposure, and the presence of dIgA led to an increase in virions in mesenteric lymph nodes. Taken together, these technologies enable in vivo and in situ visualization of antibody-virus interactions and detailed investigations of early events in HIV infection., Author summary Vaccines provide protection in humans by eliciting the production of antibodies when exposed to a specific pathogen. Currently, an effective human immunodeficiency virus (HIV) vaccine does not exist. Since the beginning of the HIV epidemic, approximately 38 million people have died, creating the need to develop an HIV vaccine. The most common antibody in the organs that are exposed to HIV is dimeric IgA (dIgA). Here, we used multiple imaging techniques to determine how HIV travels throughout the colon once introduced into the body and how dIgA influences HIV movement in the rectum. We found that dIgA increased the amount of HIV found in the colon, the distance it travelled, and the depth into tissues that HIV penetrated. dIgA also increased the amount of HIV in the mesenteric lymph nodes two hours after viral exposure. Our study shows these imaging technologies can be used to examine interactions between viruses and antibodies in early HIV infection in the natural context of the anatomy and physiology of the rhesus macaque model.

Vertical transmission of human immunodeficiency virus (HIV) can occur in utero, during delivery, and through breastfeeding. We utilized Positron Emission Tomography (PET) imaging coupled with fluorescent microscopy of 64Cu-labeled photoactivatable-GFP-HIV (PA-GFP-BaL) to determine how HIV virions distribute and localize in neonatal rhesus macaques two and four hours after oral viral challenge. Our results show that by four hours after oral viral exposure, HIV virions localize to and penetrate the rectal mucosa. We also used a dual viral challenge with a non-replicative viral vector and a replication competent SHIV-1157ipd3N4 to examine viral transduction and dissemination at 96 hours. Our data show that while SHIV-1157ipd3N4 infection can be found in the oral cavity and upper gastrointestinal (GI) tract, the small and large intestine contained the largest number of infected cells. Moreover, we found that T cells were the biggest population of infected immune cells. Thus, thanks to these novel technologies, we are able to visualize and delineate of viral distribution and infection throughout the entire neonatal GI tract during acute viral infection., Author summary Approximately 1.8 million children are currently living with human immunodeficiency virus (HIV). While mother-to-child HIV transmission can occur in utero and during delivery, it most commonly occurs through breastfeeding, creating the need to understand how the virus moves throughout the body and infects the infant once breast milk is consumed. Here, we used multiple imaging techniques and PCR to determine how HIV distributes throughout the gastrointestinal tract after oral viral exposure and in which tissues and cell types become acutely infected. We found that HIV rapidly spreads throughout and penetrates the entire gastrointestinal tract as early as four hours after exposure. We also found that the intestine contained the largest number of infected cells at 96 hours and that most cells infected were T cells. Our study shows that these imaging technologies allow for the examination of viral distribution and infection in a rhesus macaque model.

Transmission of HIV across mucosal barriers accounts for the majority of HIV infections worldwide. Thus, efforts aimed at enhancing protective immunity at these sites are a top priority, including increasing virus-specific antibodies (Abs) and antiviral activity at mucosal sites. Mucin proteins, including the largest cell-associated mucin, mucin 16 (MUC16), help form mucus to provide a physical barrier to incoming pathogens. Here, we describe a natural interaction between Abs and MUC16 that is enhanced in specific disease settings such as chronic HIV infection. Binding to MUC16 was independent of IgG subclass, but strongly associated with shorter Ab glycan profiles, with agalactosylated (G0) Abs demonstrating the highest binding to MUC16. Binding of Abs to epithelial cells was diminished following MUC16 knockdown, and the MUC16 N-linked glycans were critical for binding. Further, agalactosylated VRC01 captured HIV more efficiently in MUC16. These data point to a novel opportunity to enrich Abs at mucosal sites by targeting Abs to MUC16 through changes in Fc glycosylation, potentially blocking viral movement and sequestering the virus far from the epithelial border. Thus, next-generation vaccines or monoclonal therapeutics may enhance protective immunity by tuning Ab glycosylation to promote the enrichment of Abs at mucosal barriers.

After fusion, HIV delivers its conical capsid into the cytoplasm. To release the contained reverse-transcribing viral genome, the capsid must disassemble in a process termed uncoating. Defining the kinetics, dynamics, and cellular location of uncoating of virions leading to infection has been confounded by defective, noninfectious particles and the stochastic minefield blocking access to host DNA. We used live-cell fluorescent imaging of intravirion fluid phase markers to monitor HIV-1 uncoating at the individual particle level. We find that HIV-1 uncoating of particles leading to infection is a cytoplasmic process that occurs ∼30 min postfusion. Most, but not all, of the capsid protein is rapidly shed in tissue culture and primary target cells, independent of entry pathway. Extended time-lapse imaging with less than one virion per cell allows identification of infected cells by Gag-GFP expression and directly links individual particle behavior to infectivity, providing unprecedented insights into the biology of HIV infection.

Cervical and vaginal epithelia are primary barriers against human immunodeficiency virus type I (HIV-1) entry during male-to-female transmission. Cervical mucus (CM) is produced by the endocervix and forms a layer locally as well as in the vaginal compartment in the form of cervicovaginal mucus (CVM). To study the potential barrier function of each mucus type during HIV-1 transmission, we quantified HIV-1 mobility in CM and CVM ex vivo using fluorescent microscopy. Virions and 200-nm PEGylated beads were digitally tracked and mean squared displacement was calculated. The mobility of beads increased significantly in CVM compared to CM, consistent with the known decreased mucin concentration of CVM. Unexpectedly, HIV-1 diffusion was significantly hindered in the same CVM samples in which bead diffusion was unhindered. Inhibition of virus transport was envelope-independent. Our results reveal a previously unknown activity in CVM that is capable of impeding HIV-1 mobility to enhance mucosal barrier function.

Currently, there are mounting data suggesting that HIV-1 acquisition in women can be affected by the use of certain hormonal contraceptives. However, in non-human primate models, endogenous or exogenous progestin-dominant states are shown to increase acquisition. To gain mechanistic insights into this increased acquisition, we studied how mucosal barrier function and CD4+ T-cell and CD68+ macrophage density and localization changed in the presence of natural progestins or after injection with high-dose DMPA. The presence of natural or injected progestins increased virus penetration of the columnar epithelium and the infiltration of susceptible cells into a thinned squamous epithelium of the vaginal vault, increasing the likelihood of potential virus interactions with target cells. These data suggest that increasing either endogenous or exogenous progestin can alter female reproductive tract barrier properties and provide plausible mechanisms for increased HIV-1 acquisition risk in the presence of increased progestin levels., Author Summary Sexual transmission accounts for over 80% of all HIV-1 infections, with half of new infections occurring in women. Epidemiological studies suggest that certain hormonal contraceptives may be associated with increased HIV-1 acquisition. A hormonal influence of vaginal HIV acquisition is supported by studies utilizing various non-human primate models, which reveal that susceptibility to vaginal transmission is affected by the menstrual cycle or exogenous hormonal treatment. However, the mechanism of increased susceptibility remains unknown. Here, utilizing a variety of techniques and non-human primates, we illustrate that progestin-based contraceptives, such as Depo-Provera, and the natural menses luteal phase have a very similar impact in these models systems. Both increase virus influx into the endocervix and stimulate target cell infiltration of the squamous epithelium. The shedding of the superficial dead layers of the squamous epithelium in the progestin dominant state put the tissue resident cells in close proximity with virus in the lumen increasing the possibility of interactions and infection. A better understanding of vaginal SIV/SHIV acquisition in these widely utilized models is essential to interpret the results of ongoing clinical trials of HIV-1 acquisition during hormonal contraceptives use. An increased understanding of the mechanisms of HIV acquisition should contribute to vaccine development.

The decrease in HIV acquisition after circumcision suggests a role for the foreskin in HIV transmission. However, the mechanism leading to protection remains undefined. Using tissue explant cultures we found that Langerhans cells (LCs) in foreskin alter their cellular protein expression in response to external stimuli. Furthermore, we observe that upon treatment with TNF-alpha, tissue-resident LCs became activated and that stimulatory cytokines can specifically cause an influx of CD4+ T-cells into the epithelial layer. Importantly, both of these changes are significant in the inner, but not outer, foreskin. In addition, we find that LCs in the inner foreskin have increased ability to sample environmental proteins. These results suggest differences in permeability between the inner and outer foreskin and indicate that HIV target cells in the inner foreskin have increased interaction with external factors. This increased responsiveness and sampling provides novel insights into the underlying mechanism of how circumcision can decrease HIV transmission.

The majority of human immunodeficiency virus type 1 (HIV-1) transmission events occur in women when semen harboring infectious virus is deposited onto the mucosal barriers of the vaginal, ectocervical, and endocervical epithelia. Seminal factors such as semen-derived enhancer of virus infection (SEVI) fibrils were previously shown to greatly enhance the infectivity of HIV-1 in cell culture systems. However, when SEVI is intravaginally applied to living animals, there is no effect on vaginal transmission. To define how SEVI might function in the context of sexual transmission, we applied HIV-1 and SEVI to intact human and rhesus macaque reproductive tract tissues to determine how it influences virus interactions with these barriers. We show that SEVI binds HIV-1 and sequesters most virions to the luminal surface of the stratified squamous epithelium, significantly reducing the number of virions that penetrated the tissue. In the simple columnar epithelium, SEVI was no longer fibrillar in structure and was detached from virions but allowed significantly deeper epithelial virus penetration. These observations reveal that the action of SEVI in intact tissues is very different in the anatomical context of sexual transmission and begin to explain the lack of stimulation of infection observed in the highly relevant mucosal transmission model. IMPORTANCE The most common mode of HIV-1 transmission in women occurs via genital exposure to the semen of HIV-infected men. A productive infection requires the virus to penetrate female reproductive tract epithelial barriers to infect underlying target cells. Certain factors identified within semen, termed semen-derived enhancers of virus infection (SEVI), have been shown to significantly enhance HIV-1 infectivity in cell culture. However, when applied to the genital tracts of living female macaques, SEVI did not enhance virus transmission. Here we show that SEVI functions very differently in the context of intact mucosal tissues. SEVI decreases HIV-1 penetration of squamous epithelial barriers in humans and macaques. At the mucus-coated columnar epithelial barrier, the HIV-1/SEVI interaction is disrupted. These observations suggest that SEVI may not play a significant stimulatory role in the efficiency of male-to-female sexual transmission of HIV.

Worldwide, HIV-1 infects millions of people annually, the majority of whom are women. To establish infection in the female reproductive tract (FRT), HIV-1 in male ejaculate must overcome numerous innate and adaptive immune factors, traverse the genital epithelium, and establish infection in underlying CD4 + target cells. How the virus achieves this remains poorly defined. By utilizing a new technique, we define how HIV-1 interacts with different tissues of the FRT using human cervical explants and in vivo exposure in the rhesus macaque vaginal transmission model. Despite previous claims of the squamous epithelium being an efficient barrier to virus entry, we reveal that HIV-1 can penetrate both intact columnar and squamous epithelial barriers to depths where the virus can encounter potential target cells. In the squamous epithelium, we identify virus entry occurring through diffusive percolation, penetrating areas where cell junctions are absent. In the columnar epithelium, we illustrate that virus does not transverse barriers as well as previously thought due to mucus impediment. We also show a statistically significant correlation between the viral load of inocula and the ability of HIV-1 to pervade the squamous barrier. Overall, our results suggest a diffusive percolation mechanism for the initial events of HIV-1 entry. With these data, we also mathematically extrapolate the number of HIV-1 particles that penetrate the mucosa per coital act, providing a biological description of the mechanism for HIV-1 transmission during the acute and chronic stages of infection.

Background Previously, we illustrated that HIV is able to penetrate the intact female genital mucosal barrier. We found that HIV penetrates to depths where target cells reside. Using data obtained from tissues of more than 40 donors, we are able to generate an average for the ability of HIV to penetrate the mucosal. Using these averages we can extrapolate the number of HIV particles penetrating the mucosa per coital act for male to female HIV transmission for both acute and chronic infections.

To gain insight into female-to-male HIV sexual transmission and how male circumcision protects against this mode of transmission, we visualized HIV-1 interactions with foreskin and penile tissues in ex vivo tissue culture and in vivo rhesus macaque models utilizing epifluorescent microscopy. 12 foreskin and 14 cadaveric penile specimens were cultured with R5-tropic photoactivatable (PA)-GFP HIV-1 for 4 or 24 hours. Tissue cryosections were immunofluorescently imaged for epithelial and immune cell markers. Images were analyzed for total virions, proportion of penetrators, depth of virion penetration, as well as immune cell counts and depths in the tissue. We visualized individual PA virions breaching penile epithelial surfaces in the explant and macaque model. Using kernel density estimated probabilities of localizing a virion or immune cell at certain tissue depths revealed that interactions between virions and cells were more likely to occur in the inner foreskin or glans penis (from local or cadaveric donors, respectively). Using statistical models to account for repeated measures and zero-inflated datasets, we found no difference in total virions visualized at 4 hours between inner and outer foreskins from local donors. At 24 hours, there were more virions in inner as compared to outer foreskin (0.0495 +/− 0.0154 and 0.0171 +/− 0.0038 virions/image, p = 0.001). In the cadaveric specimens, we observed more virions in inner foreskin (0.0507 +/− 0.0079 virions/image) than glans tissue (0.0167 +/− 0.0033 virions/image, p, Author Summary Although several clinical trials have demonstrated that male circumcision can protect men from becoming infected with HIV, we know very little about how men get infected through sex and how circumcision changes this. In this study, we explored possible sites of virus transmission across the penis by looking at how HIV interacts with adult male foreskins, penile tissues from circumcised and uncircumcised cadavers, and male rhesus macaques. Using epifluorescent microscopy, we captured images of individual HIV particles entering the penile skin, sometimes to depths where CD4+ (potential target) cells could be found. We found more virus in and on the inner aspect of the foreskin than the outer aspect of the foreskin after culturing for 24 hours. Additionally, there was more virus entering the glans penis as compared to foreskin tissues from uncircumcised cadaveric donors, and to greater depths in these tissues. We made similar observations of virus entering the tissue in living rhesus macaques, strengthening the results obtained from human tissues. This information should help us better understand how the virus moves into uncircumcised penile tissue placing uncircumcised men at higher risk for HIV infection during sex.

The majority of new HIV infections occur in women as a result of heterosexual intercourse, overcoming multiple innate barriers to infection within the mucosa. However, the avenues through which infection is established, and the nature of bottlenecks to transmission, have been the source of considerable investigation and contention. Using a high dose of a single round non-replicating SIV-based vector containing a novel dual reporter system, we determined the sites of infection by the inoculum using the rhesus macaque vaginal transmission model. Here we show that the entire female reproductive tract (FRT), including the vagina, ecto- and endocervix, along with ovaries and local draining lymph nodes can contain transduced cells only 48 hours after inoculation. The distribution of infection shows that virions quickly disseminate after exposure and can access target cells throughout the FRT, with an apparent preference for infection in squamous vaginal and ectocervical mucosa. JRFL enveloped virions infect diverse CD4 expressing cell types, with T cells resident throughout the FRT representing the primary target. These findings establish a new perspective that the entire FRT is susceptible and virus can reach as far as the ovary and local draining lymph nodes. Based on these findings, it is essential that protective mechanisms for prevention of HIV acquisition must be present at protective levels throughout the entire FRT to provide complete protection., Author Summary There is currently a great effort world-wide to develop interventions such as vaccines and microbicides to decrease, or hopefully block, HIV transmission. To model the infection of women, the field utilizes the rhesus macaque vaginal transmission model. Understanding the initial events leading to infection after viral challenge of the female reproductive tract (FRT) is crucial for the development of functional prevention strategies. To this end, we developed a novel method for detecting infection in the rhesus macaque FRT after vaginal inoculation. This method utilizes single round replication defective vector that expresses dual reporter proteins, Luciferase and mCherry. Monitoring Luciferase expression allows us to identify the sites of infection within the intact FRT, while fluorescent protein mCherry allows us to visualize the single infected cells. Our studies revealed that virus can access the entire upper and lower reproductive tract. Infection occurs primarily in vaginal and ectocervical tissue, but can spread as far as the ovary and local draining lymph nodes. All classically defined susceptible cell types can be infected with the broadly tropic HIV envelope utilized in this study. Prevention strategies aimed at protecting from HIV infection should consider the entire FRT architecture as potentially susceptible and design interventions accordingly.

Background Currently, there is much debate on whether epithelial thinning from hormonal contraceptives can increase HIV acquisition. Previously, we illustrated that HIV can penetrate to depths in squamous epithelium where it can interact with target cells, such as CD4+ T-cells and macrophages. Using a similar approach, we show that epithelial thinning affects virus penetration, along with target cell and cellular junction distribution.